The present invention relates generally to the breeding of tomato plants. More specifically, the invention relates to the introduction of a transgene that confers a delayed ripening phenotype on tomato plants.
The plant hormone ethylene has a profound influence on plant physiology. Active in trace amounts, it affects a number of processes such as fruit ripening, seed germination, plant growth, leaf and flower senescence, pathogen infection, and the interaction of plants with their environment. In particular, ethylene induces a number of physiological changes associated with fruit ripening such as accumulation of carotenoid pigments, conversion of cholorplasts to chromoplasts, the increased expression of genes encoding cell wall degradation enzymes, fruit softening and susceptibility to pathogens.
Control of the effects of ethylene is a particularly useful approach to controlling fruit ripening in tomato. More than 80% of tomatoes (by volume) currently sold in the United States are picked while green. Growers harvest green tomatoes for several reasons: (1) green tomatoes are firmer, enabling them to withstand shipping and handling with less injury; (2) a green tomato harvest is less labor-intensive and less costly than a vine-ripe harvest and (3) green fruit stays in the field for a shorter period of time reducing the risk of loss from weather or pests.
After harvest, either the packer or the repacker exposes the green tomatoes to an external source of ethylene gas to cause the tomatoes to develop red color. This practice reddens the fruit, but these tomatoes will not always develop full flavor when picked at the green stage. Fruit that have begun to ripen need to be shipped at a low temperature to delay ripening, however these low temperatures decrease fruit quality. Frequently, a portion of the green fruit is harvested at the immature green stage, which means that it will never achieve full ripeness even with the application of ethylene. Such tomatoes, together with other distribution-damaged tomatoes, do not achieve full flavor potential and, we believe, are a major factor contributing to consumer dissatisfaction with current fresh market tomatoes.
In tomato (and other so called climacteric fruit), fruit ripening is associated with a burst of respiration and a concomitant increase in ethylene production. Once ripening is initiated, the endogenous ethylene production rises autocatalytically.
If ethylene production could be controlled, tomato fruit could be left on the vine longer to develop the fruit components which contribute to flavor. The present invention addresses these and other needs.